THE COMMA Use a comma in front of 'coordinating conjunctions' to combine two complete sentences When combining two complete sentences, both Finnish and English agree that you should put a comma before coordinating conjunctions, such as and, but, nor, yet, or, and so. The subjects in the two separate sentences are underlined in the examples below. Sentence 1 + [coord. conj.] + sentence 2: As a result of global warming, the oceans will warm, and glaciers will melt. NASA has used fuel cells to generate electricity in spacecraft since the 1960s, but more research is needed to make them durable and cost-effective for use in cars, homes, or businesses. Hydrogen is non-toxic and non-poisonous. It will not contaminate groundwater, nor will a release of hydrogen contribute to atmospheric pollution. Hydrogen fuel cells are safe and effective, yet the technology is still too expensive for the mass market. Hydrogen is the most plentiful gas in the universe, so there is no fear of this energy source ever running out.   When both sentences have the same subject, English tends to delete the second subject, and no comma is then placed before the coordinating conjunctions. With comma: These schemes provide a solution to current traffic problems, and they are easy to implement. [subject]   [same subject]   Without comma: These schemes provide a solution to current traffic problems and    Ø are easy to implement. [subject] [no subject]   However, if one subject has two verbs, then no comma is placed before the coordinating conjunction of the second verb. Different subjects: Hydrogen fuel cells are safe and effective, but the technology is still too expensive for the mass market. Same subject: Hydrogen fuel cells are safe and effective but still too expensive for the mass market.

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